what this is little snippet is supposed to repersent is when you press the "UP" button jumping is set to true which them runs this which sets yVel to = and then decreases it by 30 (which allows the player to move in the upwards direction for by 30. However when it hits -100 it knows you have jumped high and starts decreasing your yVel to fall back to the ground. But what is actully happening is the Player(myDot) is just forever going in the upwards position even though i have set it to stop at -100.

i realize i have completely over complicated that but you get the picture

EDIT: Actually your first problem is that by setting yVel to 0 first, and then doing yVel -= 30, you will always be setting it to -30, and never to anything below that. You should set your yVel to 0 when the key up event is received, instead of in your main loop.
Note that if you hold down a key, you may constantly receive events for that key. So your keyhandling should be:

Also, what do you mean by "it just holds the value of the player speed it doesn't increase" - I don't understand?

Are you sure that those values you've set (the -100 limit) won't cause the player to move off the top of the screen anyway? Why not put some std::cout statements and check how your yVel is changing in the main loop?

Edit: i have kinda fixed it when i press space and enter the jumping statement my yVel goes from 0 to -120 and moves -120 y's but then it changes back to 0 so he dosent come down. Here is my updated code

Edit: i have kinda fixed it when i press space and enter the jumping statement my yVel goes from 0 to -120 and moves -120 y's but then it changes back to 0 so he dosent come down. Here is my updated code

Following each iteration through there, it looks to me like this:
1. yVel gets -= 120, and should now be -120 (assuming you set it to 0 when jumping)
2. yVel <= -240 evalutes to false, code moves to next loop
3. yVel gets -= 120, and should now be -240
4. yVel <= -240 evaluates to True - you enter the if statement
5. yVel gets += 240 - and now becomes 0
6. jumping is set to false, nothing more is executed in that part

If you want to set your velocity to some downward velocity (like positive 240) once it reaches a maximum, you should do two things:
a) make the statement yVel += 240 be just yVel = 240;
b) make the check yVel <= 240 be yVel < 240
- doing these will results in your yVel being -120, -240, 0 (after each execution of your loop).
Hope that helps, because I'm still not 100% clear on how you're using your yVel.